Torrey, Utah, was chosen for the workshop’s venue because of its proximity to Lake Powell, the reservoir behind the Glen Canyon Dam, where low water levels have exposed a majority of the delta where the Colorado River enters the reservoir.
These low water elevations (see graph) result from a combination of five years of drought throughout the west, and the Dam operator’s legal obligation to release fixed amounts of water into the lower Colorado basin.
In the 1920’s, the Colorado River Compact was signed, a multi-state agreement regulating who gets to use what part of the flow. As part of this agreement (and a later agreement with Mexico), hydrologists came up with an estimate of the Colorado’s average discharge, and the Agreements stated that the Glen Canyon dam had to release half of that amount into the downstream system. Unfortunately, the agreement stipulated a fixed quantity (regardless of actual discharges), and the period the hydrologists used was an unusually wet one. So for most of the years since, the Glen Canyon dam has actually released more than half of the water it received. For years, this was not a problem as the upstream demands were being met anyway. Then significant growth came to Denver, Salt Lake City and other communities in the northern parts of the system, and finally, five years of drought.
While water released from the reservoir continued at a fixed level, inflows to Lake Powell during the five years from 9/99 through 9/04 were 62%, 59%, 25%, 51% and 49% of average. The 25% of average mark in 2002 was an all-time low for water inflows since the dam's completion. As a result of these two factors, the water surface elevation of Lake Powell fell to 3,555 feet in April of 2005 (just after the workshop). At that time, the reservoir was at a mere 33% of capacity.
John Dohrenwend of Southwest Satellite Imaging led workshop attendees on a field trip to the emergent Lake Powell delta. The group went to the (former) Hite Marina and walked out onto the delta from there, and had a unique opportunity to observe the effects of delta surface processes first hand. A planned boat tour had to be cancelled because boat ramp operators at the upstream end of the reservoir were unable to keep up with the falling water levels (by extending ramps or relocating them).
Dr. Dohrenwend has been using satellite imagery and ground photography to document the delta’s emergence and subsequent evolution, and he presented some of his work to the group (see some samples in the image gallery). In addition, Lincoln Pratson of Duke University presented some of his ongoing research into that portion of delta still underwater.
